An illuminated keyboard is a keyboard with a lighting means to illuminate keys. FIG. 1 is a schematic exploded view illustrating a key of a conventional illuminated keyboard. The key 90 of the conventional illuminated keyboard comprises a circuit board 94, a light-emitting element 91, a key housing 92, a light-transmissible channel 921 and a keycap 93. The key housing 92 and the keycap 93 are located over the circuit board 94. The light-emitting element 91 is installed on the circuit board 94. For example, the light-emitting element 91 is a light emitting diode. Moreover, the light-transmissible channel 921 runs through the key housing 92. A light beam 911 emitted by the light-emitting element 91 passes through the key housing 92 via the light-transmissible channel 921. Moreover, a light guide structure 922 is formed in the light-transmissible channel 921 for assisting in guiding the light beam 911. Consequently, the light beam 911 is outputted from the keycap 93, and an illuminating function of the key 90 is achieved.
However, since the opening of the light-transmissible channel 921 of the conventional key 90 is very small, the light amount of the light beam 911 passing through the light-transmissible channel 921 is low. Moreover, since the light-outputting position of the light guide structure 922 is restricted by the opening of the light-transmissible channel 921, the light-outputting position of the light guide structure 922 is small. Consequently, only a small amount of the light beam is guided by the light guide structure 922, and the portion of the light beam that is guided to the outside of the light guide structure 922 is centralized to the periphery region around the opening of the light-transmissible channel 921. Under this circumstance, the light beam 911 cannot be uniformly diffused to the surroundings through the keycap 93, and thus the light beam cannot be effectively guided. Moreover, while the light beam passes through the inner portion of the key, a portion of the light beam is lost. Since a great amount of the light beam is wasted, the illuminating efficacy is impaired. Therefore, the conventional illuminated keyboard and its key need to be further improved.